Originally Answered: Did we contaminate Mars with life?
Hopefully though, any remaining viable organisms are only on the surfaces of the spacecraft or within the spacecraft, and haven't spread or been blown in the winds to other parts of Mars.
The modern rovers are well sterlized. But it has not been possible to eliminate all spores, they just have a target of a maximum number of spores per square meter of the spacecraft surface.
So - they certainly still have viable spores on the spacecraft surfaces. It is just that the numbers of spores are very low. and luckily the surface of Mars is also very inhospitable, though there might be some niches that extremophiles could survive in.
Also the computer components aren't sterlized at all because that is impossible to do without destroying them. They are just enclosed with filters to keep any micro-organisms within. Since the Mars environment has dust storms, the rovers will be eroded eventually, if slowly. Spores also are very long lived, can be millions of years. So there will be viable spores on Mars for millions of years into the future as a result of our missions to the planet.
So the question really is - has any of this life escaped, or will it escape, and can any of it actually thrive on the surface.
There have been several mishaps and crashes that could have lead to this happening.
The Mars Climate Orbiter- the one that famously crashed on Mars due to a mix up about metric and imperial units - wasn't intended to land on Mars, and so was only sterilized to Category III. Though it may have burnt up completely during entry, there is a possibility that some of it survived the entry and contaminated the surface of Mars.
Many other historical Mars missions have crash landed and some of these crashes might have created other possible opportunities for forward contamination. Another fairly recent example from NASA is the Mars Observer, intended as an orbital mission, which also crashed on Mars
Even the Viking missions, noted for the care taken to prevent forward contamination of Mars, still weren't sterilized to quite the same levels as modern missions to Mars. Some of the early Soviet Union missions which included several landers in the Soviet Union - Mars series, were probably sterilized to less than the Viking levels.
The COSPAR policy guidelines are based on probabilities, and in 1969 the guideline was that there should be a probability of less than 1 in 1000 of contaminating Mars during the period of biological exploration. However due to issues in the models used, the probability of contamination may be higher than this.
So, yes, it is possible that Mars has already been contaminated with Earth life. However, on the positive side, the surface of Mars is inhospitable for most forms of Earth life. Also though the Mars storms eventually degrade materials on the surface of Mars, this is a far slower process than on Earth. The sealed units are also likely to remain sealed over long timescales (except for the possible case of crashed spacecraft).
The original aims of COSPAR are that the surface of Mars remains uncontaminated at least during the current scientific exploratory phase, including the search for signs of life or proto-life on Mars. Christopher McKay has argued further, that until we understand the situation better, we must explore Mars in a way that is biologically reversible, so that we can remove all life forms carried to the planet by our explorations.
Previous missions to Mars, such as the Pathfinder mission and the two MER rovers, have carried microorganisms to the Martian surface where they remain dormant as long as shielded from ultraviolet radiation. To reverse this contamination already present on Mars, it would be necessary to collect all metal objects within which microbes could remain viable. Furthermore, the soil at crash sites and in the vicinity of landers that had come into contact with the spacecraft would have to be thrown up into the atmosphere where it would be exposed to sterilizing ultraviolet radiation. A similar approach can be used to reverse the contamination from human bases.[102]So anyway reasonably hopeful so far that the introduced life has remained confined to the spacecraft, though can't be certain.
As to whether it could thrive on the surface, recent experiments have shown extremophiles to be more hardy than expected. They have survived conditions similar to the surface of Mars for months in tests. Lichens have been shown to photosynthesize in Mars conditions just using the small amount of moisture you can get from morning and evening dew.
Some extremophiles could survive in thin films of salty brine - it's not known if these films occur on Mars but it is possible that they do, possibly a little way below the surface - in some places on Mars. There may also be caves and other underground habitats that introduced life could survive in, and reproduce.
So, if we do detect life on Mars, follow up observations will be needed to make sure it isn't life previously introduced by earlier missions to Mars. If it ever does turn out that despite our best efforts, Earth life has been introduced to Mars, it is still important not to introduce any more new species to the planet until we understand better what the implications are (e.g. for terraforming or for research into the geology of Mars)
Yes it's true that the Earth and Mars have exchanged material and spores, and some of those might well have survived the journey and reproduced on Mars. That's sometimes taken as meaning that planetary protection is unimportant.
But - the last such exchange might have been as long ago as the huge meteorite that lead to extinction of the dinosaurs. It might never have happened even - transfer of life yes surely - but might have never reproduced on Mars.
So - Mars is as separated from the Earth as the continents on Earth are separated from each other for most animals. Introducing micro-organisms to Mars is likely to be at least as disruptive as introducing rabbits to Australia.
It could be much more disruptive if the life on Mars has a different chemical basis, or there is no life there at all and only remnants of early proto-biology - which we could learn much from if it is left uncontaminated..
Also if we decide to terraform Mars, then introduced life could disrupt that process too. E.g. aerobes taking oxygen out of the air as fast as we try to add it. It might be necessary to introduce micro-organisms in a careful sequence. We are a long way from the level of understanding and technology to terraform Mars at present in my opinion. But unplanned, accidentally introduced life could make any such future attempt very hard to do.
(much of this is from the section on the wikipedia article Manned Mission to Mars - I contributed the Critique section of that article). You can find references to all these things there.
Manned mission to Mars - has Mars been contaminated already
Manned mission to Mars - Critique
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
4.8m answer views110.4k this month
Top Writer2017, 2016, and 2015
Published WriterHuffPost, Slate, and 4 moreHuffPost, Slate, Forbes, Newsweek, Business Insider, and Science 2.0